The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, in automatic transmission field, achieving more shift stages is a technology for improving fuel consumption and driving efficiency and has been researched, and recent increases in oil prices are triggering hard competition in enhancing fuel consumption of a vehicle.
In this sense, research on an engine has been undertaken to achieve weight reduction and to enhance fuel consumption by so-called downsizing, and research on an automatic transmission has been performed to simultaneously provide better drivability and fuel consumption by achieving more shift stages.
In order to achieve more shift stages for an automatic transmission, the number of parts, particularly the number of planetary gear sets is typically increased. This negatively affects installability, production cost, weight, and power flow efficiency, and a total length of transmission.
The majority of general automatic transmissions having more than eight speeds also increase its total length, which has drawbacks of deteriorating installability.
As a result, plural rows structure which planetary gear sets are on planetary gear sets has been adopted, or a dog clutch is applied in place of wet control elements. However, in this case, applicable structure is restricted and shift feel is deteriorated by applying the dog clutch.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.